Dielectric gage



Sept 10, 1957 F. N. RQTHACKER 2,806,204

DIELECTRIC GAGE Filed July 20. 1951 2 sheets-sheet 1 V fwn l rffonbsk INVENToR.

WIWI/7L .L J

l cum/lr f 'HUUR/VEN! L/m/wm F. N. ROTHACKER Sept. 10, 1957 DIELECTRIC GAGE 2 Sheets-Sheet Filed July 20, 1951 h EER; mgm.

United States Patent to `a gage applicable to many It w1ll be particularly described herein in con- The invention relates fields.

nection with the continuous measurement and indica- .cation of the thickness of paper or of a coating upon a -carrier sheet or -wejb such as :of paper or measures both the thickness of the carrier and the coating thereupon. The gage is capable of measuring the thickness of .conducting 4or metallic sheets as `well as sheets of dielectric materials. In a somewhat different form it will indicate the moisture content of a continuous web of material.

-It is an object of the invention :to produce a gage for continuously measuring and indicating any variation in the dielectric v ajlue of sheet material and hence of the thickness thereof.

'Another object is -to construct .a lgage which continuously measures and indicates the .dielectric value of a coating upon a carrier or sheet material and hence of the thickness thereof.

Another object is to construct a gage for continuously measuring and indicating 4the .dielectric lvalue ofv and hence the thickness of the sheet ycarrier and of the combined thickness of the carrier and of a coating thereon.

A `still further object is to measure :the dielectric value of and hen-ce the thickness of a sheet carrier at a first point and to measure the dielectric value of and hence the combined thickness of the carrier and a coating thereupon at a point spaced from the first point and to subtract the first measurement `or indication from the second to give a measurement and indication of the thickness -of the coating.

Another object is to construct a gage which indicates the ,dielectric v alue of rand hence the thickness of a sheet material and provides-a continuous comparison thereof with fone or more standards thereof.

Another ,object is to continuously indicate the moisture content of a web or sheet of material by a new andnovel mechanism.

Other objects of the invention will be more apparent from the following description when taken .in connection with the accompanying ,drawing illustrating some preferred embodiments thereof in which:

Figure l is a view of a coating machine with the dielectric gage diagrammatica-lly illustrated in connection therewith;

Figure 2 is an enlarged side view yof a scanning roll, capacitive adjusting means and Ystandard comparator means in position for indicating thickness of sheet.

Figure 3 is .a diagrammatic end view of `a scanning roll and the comparator means in comparator indicating position',

Figure 4 is an enlarged view of the capacitive adjusting means;

Figure 5 is a view of the signal or beam trace on the cathode ray tube;

Figure 6 is a side view of a scanning roll having a single spiral scanning bar, the circumferential dimension of which is a little less than 360.;

Figure 7 is a View of the trace on the cathode ray ICC tube for ia Vcoating which does not extendv completely across the width of Athe carrier sheet or paper;

Figure 8 is a diagrammatic view of the circuit for controlling vertical deflection of a scope;

Figure 9 is a circuit diagram of that portion of the circuit for vertical deliection of the indicator or Ascope' having signal delaying means;V i l Figure l0 is a view showing the vtrace when .the die electric gage is yused to determine .thickness and moisture content of a sheet of material utilizing two frequencies;

Figure 1l is a 'chart for determining the thickness and moisture content of a `web from the scope trace;

Figure 1'2 shows diagrammatically a black-.out means for the cathode ray tube for alternate revolutions of the scanning roll of Figure '6;

Figure 13 shows `the scanning elements for a gage for gaging thickness and moisture content of a web of material;

'Figure 14 is la partial view of the fixed bar 24 support for major adjustment thereof:

Figure l5 Yis a diagrammatic view of a roller type Xed seeing means;

Figure l6 shows diagrammatically, the scanning gaging vmeans and the ixed gaging means serving as the comparator means; and

Figure v17 is -a view of a photo cell blanking circuit.

There is show n diagrammatically in Figure 1 a coating machine in which a carrier or web W, such as paper or cloth, has spread over ,the face thereof a coating of any material, such `as -a plastic in the manufacture of lino-leum, a plastic coated paper and the like. The .gage is also shown more or less diagrammatically as applied to the coating machine.

The carrier or Web W to be coated and gaged is fed through a first gaging stage orV gage 15 which gages the dielectric value of and hence vthe thickness thereof after which the coating is applied to the carrier and the coated web or sheet is Afed through a second lgaging stage or gage 16 ywhich gages the combined dielectric value of and hence the Othickness of the carrier and the coating. In the construction and operation of this form of the gage, it --is desired `to make a gage for continuously gaging or indicating the thickness of the coating upon the carrier, Briefly this is accomplished by gaging the thickness of the carrier or web, recording the signal thereof and later reproducing the same to introduce a fixed delay in its application -to an indicator determined by the time for the carrier to travel between the rst gaging stage or gage :to the second gaging stage or gage after which the tir-st signal `is in `effect subtracted from the second `so that rthe indicator shows the thickness of the coating. If it is not in accordance Awith a predetermined desired thickness or standard then the coating feed may be' adjusted to correct the same.

The `gage includescapacitive means between which the material to be gaged, passes and as it passes a c ontinuous measurement of its dielectric value |and hence thickness is secured by continuously measuring the capacitance and any variation in capacitance between what is in effect the plates of a condenser. Many materials may be gaged; however, the description herein will be directed principally to a sheet material constituting a carrier or web W which is coated or being coated. Variation in tthe thickness of the carrier or sheet material results in a variation of the dielectric value of the same and in turn `varies the capacity between the plates of the condenser or capacitive means. Since a sheet or coating may vary across the Width thereof, a small area is measured across the width thereof and since it is taken as the carrier is moving at high speed this gaged yarea crosses the carrier at an angle with respect tothe .edge thereof.

The capacitive means includes a straight capacitive or conductive gage member, shown as a fixed gage bar 24, although it may be a metal covered roller, adjacent or underneath scanning roll and spiral scanning gage bar means carried thereby as will be described. The two parts of the capacitive means are spaced apart so that the material, carrier or web passes therebetween. The spacing should be great enough too so that the double thickness of an over-lapping edge which secures together the end of one carrier and the beginning of another carrier may pass therebetween. Bars having a width of about 1A inch have been used and the width may vary quite widely. The spiral gage bars have a circumferential dimension of less than 180 so that there is a gap, a two inch gap has been used, between Vthe ends of the scanning bars. The scanning bar or roll may be rotated at any desired speed; however, the greater the speed the more readings and closer spaced ,readings are secured. The higher the speed of the web, the faster the scanning roll must rotate in order to secure the same @spacing between readings. For example with `the carrier running at 150 feet per minute and the two bars scanning roll turning at 60 revolutions per minute, the readings are 'about one and 4a quarter feet apart.

The capacitive means also includes a spiral scanning Ymeans or scanning gage bar means which in the construction of Figure 2 includes at least one scanning gaging bar although in the construction particularly illustrated a plurality of such spiral scanning bars are used there being illustrated two such gaging bars and 21. The spiral form is used so that a relatively short or l,small area of bar is adjacent the fixed gaging means or bar which area constitutes the gaging area and as the spiral bar rotates the gaging area moves from one edge of the carrier across the other edge. The scanning gage bars 20 and 21 are insulated in any suitable manner such as by being secured to, set in or molded into a scanning Vroll 22 of insulating material. The scanning gage bars `extend somewhat less than 180 around the circumference of the roll and have a gap between the ends of the two scanning bars the purpose of which will be explained hereinafter. If desired, one gaging bar may spiral in a reverse direction from the other as shown so that as they rotate a scanning trace is obtained -at an angle across the sheet from one edge to the other edge and 'then at an angle from that side or edge back to the first edge.

The spiral scanning means and hence the capacitive means preferably includes also means or mechanism to accurately adjust the capacity between the gage bars throughout their length. This means may take many forms. That illustrated includes a conducting means, shown as a separate member 26 although a simpler form is the end of the scanning bar as shown in Figure 6, and a second conducting means comprising a plurality of conducting members 27 each of which has adjusting means in the form of a screw 28. Twenty-eight of the conducting members 27 have been used for each of the two scanning gage bars and the area thereof has a wide range. A round member 27 of about l./z in diameter will provide suficient adjustment. The conducting means formed by the plurality of conducting members 27 have a circumferential extent corresponding to that of the spiral gage bar. With two spiral scanning gage bars as illustrated there is for each such gage bar, a rotating conducting member 26 and a plurality of circumferentially spaced and fixed conducting members 27 having 'adjustable means for each member for adjusting the position thereof. One of the conducting or adjustable capacitive means, either the plurality or the single one, is rotatable with the roller and maybe carried thereby as shown, and the other conducting means is fixed. In the construction particularly illustrated the single conducting member 26 is mounted to be rotated with the roller or Ascanning bar and its simplest form is to bend the end of the scanning bar over the end face of the rolleras shown in Figure 6. The conducting means comprising the plurality of adjustable capacitive or conducting members 27 are carried by a frame 29 which is fixed to some part of the frame of the gage. This construction provides one which is more convenient to adjust.

The adjustable capacitive means or mechanism is used to adjust the capacity between the scanning bar or bars and the fixed bar throughout the length thereof. The signal developed between the gage bars is irregular irrespective of how carefully the radial dimension of the scanning bar is ground and how carefully the fixed bar is made. The safer way to secure adjustment is to space each adjustable capacitive member 27, iive thousandths of an inch from the conducting or capacitive member 26. The'members 27 are then backed away in order to straighten out the beam trace on the scope indicator. The scanning bar or roll is rotated therefore and the signal noted on the indicator. If a high spot of capacity is indicated by the signal or trace on the scope, the adjusting screw 28 for the proper conducting member 27 is adjusted or backed away until the beam indicates a uniform level. When the signal or trace shows a constant or practically a constant level of capacity it will be properly adjusted. There will be some ripple or peaking as the scanning bar is rotated with respect to the fixed bar 24 because of the adjusting capacitance 27;

however, this is desirable because when making the initial adjustment the peaks may be counted on the scope 4and thereby determine which adjusting capacity is out of adjustment. One such capacitive adjusting mechanism or means is provided for each scanning bar and the one shown on the left of Figure 2 is for the spiral .gage bar 20 and the one on the right is for gage bar 21.

Means or mechanism may be provided to compare the carrier and the coated carrier as to its dielectric value or thickness with respect to a standard sample. This comparing mechanism comprises a rotatable comparator `bar 32 Ywhich is connected with the scanning bar or roller to be rotatable therewith. It is also located circumferentially in the gap between the ends of the scanning bar or bars. Adjacent to the path of rotation of the comparator bar 32 is a fixed conducting comparator bar 33 upon which is carried a standard sample S. Preferably one such comparator means or pair of comparator bars 32, 33 is provided for each side of the carrier, that is, the two pairs are apart from each other so that a standard pip or signal 34 is obtained at each side of the signal from the carrier or web. If the web such as paper should be thinner than shown by the standard, the ysignal 35 would have a lower level and the operator would be informed thereby to increase the thickness of the web or to decrease it in the event that the carrier web shows ra thickness greater than the standard thickness. Or if the web is not being made at the same time, it would call for adjustment of the signal on the second gage in order to give a true comparison or indication of the thickness of the coating as will be clear where this second gage is described herein.

The capacity between the scanning gage bar and the fixed gage bar, when the carrier or the coated carrier is passed therebetween, is converted into an electric equivalent such as current fiow and amplified by any suitable electronic circuit. It is preferred to use an oscillating circuit to effect the conversion and amplification and the circuit will be described more fully hereinafter.

The second gage 16 for the coated section of the carrier or web is identical with the first gage 15 described above excepting that the standard sample for comparison would be a coated sample. This second gage does not use the signal recording portion of the first gage as will be described. The signal from this second gage is applied to a vertical deliection plate of the scope or indicator. This second gage, therefore, need not be described.

hele fie Smile distance necessarily .bewees the ,loserissf the .tiret .ease 1,5 .fe sa issue .thickness .of the carrier ,er .web and ,the eed-.sage :1.6 for seein-g the Atltickiftess of the etedfcalfrrer. ln one construction this ,distance was thirteen feet so thatthe Yfirst ygage gages the ,thickness ofthe carrier Iat .a position thirteen feet in ad- {Yanee ofthe easing taking .placef thecerrer andi-,Coating 'in .the second position between which there may be `some yvariation in carrier thickness. In orderto gage .the thick- ,ness Lofthe coating being appliedto the carrier, itismecessary .to include adelay means s o that the carrier signal is applied ,to Vthe indicator or Vscope A42. simultaneously or arinneaimately lSimultaneously .et the time ehefrau Yof the `.carrierreaches .the second gaging position .o r,ator .approxi h at ely .at thirteen feet after vthe l.sig-nal .or gagging .took classi This has been accomplished by recording the Signal from the first gage. ,lhesignal is amplified through any lsuitable electronic .circuit as will be described hereill'after land this signal yis fed .to a Arecording mechanism 3.6 .which records .the signal on a tape -orwire ,3 7, an electromagnetic recording mechanism having been used. the tape ,or wire recorder traveling .at `3fm-the speed of ,the carrier, after the record ,tape has travelled 1.3 feet the pick up means 38 takes the .signal off of the record ,or Atapeso that the signal at l.the pickup I neans 38 is taken .off .just `at the time `that that portion of v the lcarrier gaged at the rrst gaging position is 4under or approximately under the l'second gaging roll at the second gaging .position. `amplifier 39 may amplify the signal from the recorder which amplified signal is applied to one o f vthe pair o f vertical `deiiecting .plates of the indicator or catho de ray tube, that is, plate 41. This time ,delay circuit or mechanism is substituted -for the amplifier tube 74 inth e .Circuit of Vl-iigure 8. YThe lsignal from the first gage is subtracted from the signal from the v second gage, `which n 1e2 1S11 re S the COU!- .bined .thickness of carrier .and coating, so `that ,the resultant signal shown on the indicator `is the thickness of the coating. This subtraction of Signals is secured by apply- Aius the amplifier signal from the pickup .meehenism 38 to one vertical beam control means such as the vertical beam control plate 4 1 of a pair .of vopposi-tely disposed vertical control plates of a cathode ray tube .42. The signal from the second gage is applied to lthe other vertical control means or the other plate 43 ofthe oppositely disposed pair of the vertical IControl plates ofthe .eathode ray tube so that the beam control between the `plates is that produced by a difference between the amplitude of the signal vfrom the second gage 4and the :signal zfrom the Vfirst gage. This resultant field or signal, therefore, is proportional to the thickness of the .coating ,upon the carrier and hence the scope indicates the thickness of the coating C on the carrier or material W.

The other pair of plates 44 of the cathode .ray tube are connected with a sweep circuit of any suitable construction, many being well known, to sweep the .beam across the tube for each scanning bar. Preferably, however, the sweep circuit includes a condenser having :fixed plates 45 and rotating plates 4 6 4cooperating therewith. The rotating plates are driven with the scanning roller so that the beam is swept across the cathode 'ray tube for one scanning bar and back again at the same speed for the other scanning bar. By driving the rotating oondenser plates from the scanning yroller or shaft, the sweep is -timed therewith. With two scanning gage bar-s as in the .Construction particularly shown, 011e signal will ...be the beam trace in one direction from one scaiirring bar and the beam trace in .the opposite direction will be the signals from the second scanning gage bar which, however, should be identical and overlap except `as to the standard pip if there is no change in thickness and the two scannings are properly adjusted.

The scanning bar may be rot-ated at any desired lspeed with respect to the speed of the carrier. The 4faster that the scanning bar rotates the more readings will be se- .cured 4.0f .the carrier thickness and :the scanning therelengthwise .of the carrier. This is nota limiting dimension andthe spacing between the repeat `cyclesor readingsmay be anything desired Vby the manufacturer of the .cer-Iier to be measured. In vfact a measurement every ,fifty feet probably gives ample information.

The electronic circuit for converting the capacity .be- Ltween .the scanning gage means Vand the fixed gage means and any variation in ycapacitance due to the dielectric .of `the material passing therebetween and the amplification .thereof is `secured by any -suitable operating circuit. The .basic circuit particularly illustrated in Figure `8 includes .an .oscillator amplifier, modulating means, amplifier means, demodulating means, and amplifier means. The entire circuit vand the modulation portion or element there- .of is introduced primarily because it is a more effective amplifier. A coil 56 is connected at one end to the .scanning means, which if adjustable capacitive means 27 are used is .connected rto this part of the scanning means, and the other end of the coil `is connected with the fixed gage means .or bar 24. The coil S6 -is coupled to coil 57 such as through a coupling coil 58 which may have a condenser in series therewith. The coil 57 has a pair of v.condensers 59 lconnected thereacross and the midpoint is connected to the cathode of the tube 62 through ground to form an oscillator. The tank or `oscillator circuit 57A, 59 is connected between the plate y60 and grid .61 .of the tube 6 2. The plate has a load resistor 63 in series therewith. Resistive means v64 is connected between the grid and ground.

The oscillator generates A.a frequency such as 5 to 10 megacycles and -`operates Von the slope of the resonance curve and Vpreferably on the high frequency side of the curve. Any variation i-n capacity between the gage means or bars, due to variations in thickness of the 4carrier or coa-ted carrier, manifests itself in a variation in the freguency of .oscillationgenerated bythe oscillatoramplier,

the result of which is to produce a variation in current iiow through the resistive means 64. This constitutes what is known as a grid dip meter although it operates as an .oscillator 1it is in eoect a sensitive amplifier.

The varia-tions in current through the resistive means 64 result in variations in the voltage at an adjustable contact 65 which is connected with Vthe mixer grid 66 of a modulator tube 67. The grid l68 of the tube is connected with a coil 69 and condenser 70 connected in parallel with each other and forms an `oscillatory circuit which generates a frequency of -about a -thousand cycles. The signal appearing on the grid 66, which is proportional to the dielectric value of the carrier Wand the thickness thereof, is used to modulate the thousand cycle oscillation generated by the oscillator circuit of this modulator. The plate 71 of the tube has load resistive means 72 connected therewith and the signal appearing on the plate is transmitted through an output connection or wire 7 3 to an amplifier, shown as a single stage or tube 74 having a contr-0l grid 79. The amplifier may be one or more stages as desired. The tube 74 is biased to pass the negative half of the signal Vapplied to its grid. The outputconnec-tion 75 of amplifier 74 is connected with the grid 76 of a second amplifier tube 77 through a demodulating means 78 which may be la crystal detector. The .output of the tube 77 -is connected with a vertical deiiecting plate 41 of the indicator or cathode ray tube 42. As previously discussed the pick-up .coil 3.8 of the tape recorder is connected, through amplifier 39, with the other vertical deflecting plate 43 `of the indicator or cathode ray tube so that the two signals subtract and hence the beam trace on the cathode ray tube is a running or continuous measurementof the thickness of the coating C on the carrier We. The tube `77 is biased .to .approximately twenty-ve formation.

. 7 Y volts beyond cutoff so that the modulation signal only or approximately this signal is amplified and transmitted to the scope. It represents about 1% of the total voltage applied to the grid resistor of the tube.

If the coating C on the carrier W does not extend completely across the sheet, which is the Way the coating is applied thereto in many cases, there is left a short margin of uncoated carrier at each edge of the sheet. With this form of coated carrier it is not necessary to make two separate gage readings nor to provide two gages since a single gage will give all the necessary inln such case, the gage may be the same as the second gage 16 with the output of the amplifying means connected with the vertical deflecting means or plate 43 of the cathode ray tube 42, and the other vertical deflecting means or plate l471 is grounded in the manner shown in Figure 6. In this case one scanning gage bar 20 or 85 alone need be provided and one of 'the standards carried by one of the. conductors 33 may be a coated standard. The trace formed upon the screen of the cathode ray tube 42 would be that shown in Figure 7 where a pip 81 is that produced by the paper standard for comparison with the level or land 82 in the trace which constitutes the measurement of the paper thickness at one edge of the carrier. The land 83 is the measurement or indication of the coated carrier after whichappears a second land or level 82 which is the thickness of the paper at the other edge of the carrier W and finally a pip 84 which is the thickness of the coated standard for comparison with the thickness of the coated carrier represented by the land or level 83. The beam may be blacked out in any way as is well known, upon the return pass thereof; however, such black out need not be provided in which case the beam provides a trace at the lowest level. The circumferential gap of over 180 between the ends of one scanning edge bar gives the same amount of time for the beam to return to the initial side of the cathode ray scope under the control of the rotating condenser means 45, 46.

The gage for a carrier or web W having a coating C thereon spaced from the edge of the carrier may use the scanning roller of Figure 6 in which a single spiral scanning gaging bar 85 is used. With this form of scanning bar the horizontal sweep circuit may be of usual form which generates a saw-tooth sweep signal which provides a rapid beam return. The horizontal sweep circuit may include a condenser 45, 46 having plates 45 rotated with the scanning roll at half the speed of the scanning roll by gears 86 in which case the horizontal traverse of the beam across and back is uniform. It may be desirable to have alternate revolutions of the scanning roll provide a scanning trace on the scope and a blackout means may be used to black out the return trace in the inbetween alternate revolutions. Such blackout means may take many forms there being shown in Figure 12,

a half disc 92 driven at half of the speed of the scanning i roll, and hence may be mounted on the shaft with the rotating condenser plates 45 of Figure 6. With a light source 93 on lone side thereof and a photocell 94 on the other side so that the light beam plays on the photocell for alternate revolutions, the light beam is cut off for the inbetween alternate revolutions. The photocell is connected in the grid circuit of the control grid of one of the tubes, such as the amplifier tube 74, as illustrated in Figure 17to drive the grid bias to cut off in one ofthe vconditions or positions of the half disc.

The' gage may be used to measure or indicate the moisture content and thickness of a web of material such as paper, cloth and the like. It has been found that applying high frequency oscillations to the sheet of two different frequencies, that the magnitude of signal or response for eachfrequency is different for the same degree or amount of `moisture and that the magnitude is different for differentamounts of moisture. Figure l1 is a chart or plot of the magnitude of deflection at two different frequencies andat different conditions of moisture content.

adsl2-o3.

Curve A is the deflection of the beam of a cathode ray tube at 9.3 megacycles applied oscillation and curve B at 35.0 megacycles. For different applied frequencies a different pair of curves must be plotted. The frequency or frequencies used for reliable results should have a ratio of at least l to 2 and the greater the ratio the more accurate are the results achieved. A ratio of 5 megacycles for one frequency and 20 to 30 megacycles for the other appears best.

For moisture and thickness gaging, the mechanism of Figure l and the circuit of Figures 8 and 9 may be used, each gage generating a different oscillation frequency applied to the scanning gage bars or generated by the first tube. A simpler construction is shown in Figure 13 where each scanning bar or its adjusting capacitive means 27a and 27b is connected to a separate coil 56a Aand 56b and each coil has the circuit of Figure 8 connected thereto which are alike except that onecircuit applies one high frequency to the wet web to be gaged and the other coil applies a different high frequency such as those referred to above. The output of one of the two circuits is applied to the'vertical defiecting plate 43 ,of the cathode ray tube 42 and the output of the other circuit is connected with the other vertical defiecting plate 41 and the trace is shown in Figure l0 from which the difference in amplitude is read directly by the space between traces. The difference between traces is applied to the chart of Figure l1 horizontally between curve A and curve B and wherever this difference lies, the moisture content lof the web is read from the left hand percent moisture indicia. The thickness of the sheetv or web is determined by reading the level of the horizontal portion of the trace for either the high or low frequency and locating the same on the curve for its respective frequency and reading the thickness from the thickness indicia on the left margin of the chart.

The fixed gage or condenser bar may be mounted in position in any suitable manner; however, it is desirable to so mount it that its spacing with the scanning roll may be given primary adjustment at various points in its length. Figure 14 illustrates one form of such adjusting means in that at spaced intervals the fixed bar 24 is secured to a cross member 97 which may be of insulating material which cross member is secured at each end to a rail 98 extending the length of the scanning cylinder by screw adjustment 99 which raises and lowers the cross member with respect to the rail and hence raises and lowers the fixed bar 24. Spacer bars 10) may be provided to retain the sheet or web above the fixed gage bar 24 so that the fixed bar will not be worn by contact with the carrier or web.

The fixed gaging means 24 may be a roller 102 as in Figure l5 if desired which because of its curvature has a capacitive effect similar to the straight stationary bar 24. The roller may be of thin metal mounted on an insulated roller o1' of solid metal, or hollow metal and is rotated at a peripheral speed the same as the carrier speed. Preferably it rotates at the same speed as the scanning roll 22. A connection may be made with the roller form of fixed gaging means by direct connection therewith; however, a capacitive connection is preferred through a fixed bar 103 mounted adjacent thereto and extending the length thereof.

An end or both ends of the scanning bar gaging means and the fixed gaging means 24 may extend beyond thc end of the web or carrier being gaged and be used as the standard gaging means as shown in Figure 16. A standard coated carrier CS may be placed or retained above one projecting or lengthened end of the fixed gage bar 24 and is scanned by the extended end of the scanning bar 20. The other end may likewise be extended or lengthened beyond the carrier and used in the same manner with an uncoated sample to proved a constant trace would kbe the 'same as that shown'in 'Figure 7.`

The gege is ,tective for thread. painted surfaces, platius, and .steel sheets which demonstrates '.s .Wi eePPllieof bilty- Since moisture aiects the die1ectric.v..ue,'auy materiel which Picks up moisture should be eased iu a room o r surroundings which are humidied to keep the atmospheric moisture conditions constant. If it is desired to. determine moisture content as Well, the use of two different frequencies may be used in the manner described.

The conducting member r2 6 and eachof the adjustable conducting members 27 are means for electrically connecting the electronic circuit, such as by capacitively coupling, with the scanning bar means 2li), `21 to the electronic circuit and fixed garging means as well as providing, when adjustable, as shown, adjustable capacitance for the scanning bar means. The spiral scanning bar also provides Aa `simple means for providing a capacitive means or area which moves across the width of the web or material passing between the gaging means. i

The gage for indicating moisture content and thickness of a moisture absorbing material or web provides also a new method of gaging these Yfactors in such material. These facts are gaged quickly, easily and continuously by applying `two different high' frequencies to the material or web each of which frequencies responds differently to the moisture in the material, The difference in the response of the material at the two frequencies is ,then compared with previously determined differences in response of samples `of the same material and of known moisture content enables the content to be quickly determined or -readfrom a chart such as Figure 11. The level of response cf either frequency when 'compared with a standardY previously determined and recorded such as the curves on the chart give the thickness of the material.

The capacitive adjusting means for the gaging bar-s 20, 2 4 formed by the conducting member 26 and the plurality of conducting members 27 is shownV connected with,

such as by capacitive coupling, the scanning gaging bar.

The pluralityof adjustable conducting members may be connected with either gagebar since -itis immaterial which of the gage bars has its capacity modified or adjusted in order to adjust the capacity 'between bars, and the rotating conducting member 26 serves as a commutator to coact with the propel adjusted conducting member 27. The conducting members 27 in being connected .to the scanning bar end of the coupling coil, serve two functions for which -otherwise separate elements must :be provided for each function. The two functions are vfirst they provide a connecting or capacitive coupling Ameans with the rotating scanning bar and secondly by'breaking -the means up into separate members and adjusting each lmember, the members provide adjustable capacitive means -for the capacity between the two gaging bars or means. Also each adjustable conduct-ing member in e'ect provides -la series of spot readings across the width ofv the material or Ascanning bar by each peak observed on :the cathode rayltube or scope for each adjustable member which `peak enables an installer to quickly .determine by counting peaks to any high peak or peaks, the adjustable member which gave' that high peak and hence needs adjusting.

This invention is` presented to fill a -necdi-for improvements in -a dielectric gage. It is understood .that various modifications in structure, as well as changes in .mode of operation, assembly, and manner of useyniay and often do occur to those skilled in the art, especiallyafter benefiting from the teachings of Ian invention. Hence, it will be understood that this disclosure is illustrative of' preferred meansl of embodying the -inventi-on in useful form by explaining the construction, operation and advantages thereof.

What is claimed is:

l. A gage to measure variations in a material comprising capacitive means including a fixed gag'ing means Vof substantial lengthand scanning gagingbarme'ans ofV spiral form mounted for rotation'fadja'cent vthe .fixed ga'ging means and spaced therefrom Ato pass a material therebetween; an ,electronic amplifying circuit connected with the scanning easing bar meaus and they tilted gege vbar .responsive to the capacity between Athe means due to the material passing therebetween, indicator means connected with the electronic circuit to `indicate variations in capacity between the gaging means due to variations .in the material passing therebetween, capacitive adjusting means comprising a plurality of circumferentially spaced conducting members, adjusting mechanism for each member, and a circumferentially short conducting means, one of said means being connected with the scanning bar means for rotation therewith and electrically connected there with, and the other means being fixed adjacent the path of rotation of the rotatable means and electrically connected with the fixed gaging bar means.

2. 4A sage to .measure variations in e .material com: prising capacitive means Vincluding a dxed gauging Vmeans of substantial length and `scanning gaging bar means o f spiral form mounted for rotation adjacent the fixed gaging means and spaced ytherefrom .to Dass a material .therebetween; an electronic amplifying circuit connected with the scanning gaging bar means and the xed gage Vbar responsive to the capacity between the means due to the material passing therebetween, indicator means connected with the electronic .circuit .to indicate variations in capacity between the ,gaging means Vdue to variations in the material passing therebetween, capacitive adjusting means for each spiral scanning bar means comprising a circumferentially short conducting member connected with each scanning bar means for rotation `therewith and electrically connected therewith, and a plurality of circumferentially .spaced `adjustable members `for each v.seauning bar mounted `adjacent to `the path of rotation of the rotating conducting lmember and electrically connected With the fixed gaging means.

v3. A sage .to measure variations .in .a .material .comprising capacitive means including a fixed gaging means `of substautialleusth aud scanning' .easing hermosas of spiral form mounted 4for rotation4 .adjacent the rfixed gestos means and spaced therefrom to pass a material .therebetween; an electronic amplifying .circuit connected with the scanning easing .ber means and 4the fixed sage bar responsive to the capacity between the means due to the material passing therebetween, indicator means connected with ,the .electronic .circuit .to .indicate variations iu capacity between the gaging means Vdue to variations in the materiel passing therebetween, at ,leest one standard comparator mechanism comprising a rotatable Ycomparator bar of short `circumferential dimension and connected with the vscanning Mbar means `for vrotation therewith and located in a circumferential gap of the scanning bar means; a fixed comparator bar of short circumferential dimension Vlocated to be passed by the rotatable comparator bar as it rotates, and means connecting the .comparator .bars .with .the...e.1ec.t.rouie .circuit `4. A gage to measure variations in a material comprising capacitive means including a fixed gaging means of substaltialzlength and scanning gaging bar means of spiral form mounted for rotation adjacent the .fixed gaging means and spaced therefrom to pass a material therebetween; an .electronic amplifying circuit connected with the scanning .easing ber .means and the fixed gage bar responsive to the capacity `between the means due Yto the material passing ttu'erelcetweenJ .indicator .means connected with .theI electronic .circuit to .indicate variations in capacity .betweeu .the easing ,Ineens .due to variations iu the material passing therebetween, adjustable capacitive mechanism foreach spiral scanning bar comprising a first conducting means, and a second means including a plu-- rality of circumferentially spaced conducting members, adjusting ,rrfechanism for each conducting member to adjust the .position thereoftowards and away from the first conducting means, one of said means being connec-ted 4with the Yscanning gage bar means for rotation therewith and electrically .connected therewith, and the other means being fixed adjacent the path of rotation of the rotating means and electrically connected with the fixed gaging bar; at least one standard comparator mechanism comprising a rotating comparator bar of short circumferential dimension connected with the scanning gage bar means for rotation therewith and located in a circumferential gap of the scanning gage bar means, a fixed comparator bar of short circumferential dimension located to be passed by the rotatable comparator bar as it rotates, and means electrically connecting the comparator bars with the electronic circuit.

5. A gage to measure variations in a material comprising capacitive means including a fixed gaging means of substantial length and scanning gaging bar means of spiral form mounted for rotation adjacent the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic amplifying circuit connected with the scanning gaging bar means and the fixed gage bar responsive to the capacity between the means due to 'ne material passing therebetween, indicator means connected with the electronic circuit to indicate variations in capacity between the gaging means due to variations in the material passing therebetween, adjustable capacitive means comprising a plurality of circumferentially spaced conducting members, adjusting mechanism for each member, and a circumferentially short conducting means, one of said means being connected with the scanning gage bar means for rotation therewith and electrically connected therewith, and the other means being fixed adjacent the path of rotation of the rotating means and electrically connected with the fixed gaging bar; and a plurality of comparator mechanisms each comprising a rotating comparator bar of short circumferential dimension connected with the scanning gage bar `means for rotation therewith and located in a circumferential gap of the scanning gage bar means, a fixed comparator bar of short circumferential dimension located to be passed by the rotatable comparator bar as it rotates, and means electrically connecting the fixed comparator bars with the electronic circuit.

6. A gage to measure variations in a material comprising capacitive means including a fixed gaging means of substantial length and scanning gaging bar means of spiral form mounted for rotation adjacent the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic amplifying circuit connected with the scanning gaging bar means and the fixed gage bar responsive to the capacity between the means due to the material passing therebetween, indicator means connected with the electronic circuit to indicate variations in capacity between the gaging means due to variations in the material passing therebetween, capacitive adjusting mechanism for the scanning bar means comprising a circumferentially short conducting member connected with each scanning `bar for rotation therewith `and electrically connected therewith, a plurality of circumferentially spaced conducting members for the scanning bar means and mounted adjacent to the path of rotation of the short conducting member, and electrically connected with the fixed gaging bar, means to adjust the position of each circumferentially spaced member, at least one standard comparator mechanism comprising a rotatable comparator bar of short circumferential dimension and connected with the scanning bar means for rotation therewith and located in a circumferential gap of the scanning bar means, a fixed comparator bar of short circumferential dimension located to be passed by the rotatable comparator bar as it rotates, and means electrically connecting the comparator bar with the electronic circuit.

7. A gage to measure variations in a material comprising capacitive means including a xed gaging means and scanning gaging means having a plurality of gage bars of spiral form and each bar being circumferentially spaced from the other scanning'gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gage bar means and the fixed gaging means responsive to the capacity between the gage bars due to the material passing therebetween, and indicator means connected with the electronic circuit to indicate the capacity between the capacitive means due to the material passing therebetween; the indicator means being a cathode ray tube, and horizontal sweep means for the cathode ray tube including a condenser having plates rotatable with the scanning bars and controlling the sweep of the beam.

8. A gage to measure variations in a material coniprising capacitive Ymeans including a fixed gaging means and scanning gaging means having a plurality of gage bars of spiral form and each bar being circumferentially spaced from the other scanning gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gage bar means and the fixed gaging means responsive to the capacity between the gage bars due to the material passing therebetween, and indicator means connected with the electronic circuit to indicate the capacity between the capacitive means due to the ma= terial passing therebetween; capacitive adjusting mechanism for each scanning bar comprising adjusting means including a plurality of circumferentially spaced adjustable members, and a circumferentially short conducting means, one of said means being connected with the scanning bar for rotation therewith and the other means being fixed adjacent the path of rotation of the means which is rotatable, and the rotatable means being electrically connected with the spiral scanning bar and the fixed means being electrically connected with the fixed gaging bar.

9. A gage to measure varia-tions in a material comprising capacitive means including a fixed gaging means and scanning gaging means having a plurality of gage bars of spiral form and each bar being circumferentially spaced from the other scanning gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gage bar means and the fixed gaging means responsive to the capacity between the gage bars due to the material passing therebetween, and indicator means connected with the electronic circuit to indicate the capacity between the capacitive means due to the material passing therebetween; capacitive adjusting means for each spiral scanning bar comprising a circumferentially short conducting member rotatable with each scanning bar, and a plurality of circumferentially spaced adjustable members for each scanning bar and mounted adjacent to the path of rotation of the short conducting member, the conducting member being electrically connected with the scanning bar and the circumferentially spaced adjustable members being electrically connected with the fixed bar.

10. A gage to measure variations in a material comprising capacitive means including a fixed gaging means and 4scanning gaging means having a plurality of gage bars of spiral form and each bar being circumferentially spaced from the other scanning gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gage bar means and the fixed gaging means responsive to the capacity between the gage bars due to the material passing therebetween, and indicator means connected with the electronic circuit to indicate the capacity between the capacitive means due to the material 'passing therebetween; a circumferential gap bev tween each scanning gage bar including at least one standard comparator mechanism comprising a rotatable comparator barof short circumferential dimension and connected with the scanning bar for rotation therewith and located in a circumferential gap between the scanning bars; a fixed comparator bar of short circumferential dimension located to be passed by the rotatable comparator bar as it rotates, and means connecting one of the comparator bars with the electronic circuit.

1l. A gage to measure variations in a material comprising capacitive means including a fixed gaging means and scanning gaging means having a plurality of gage bars of spiral form and each bar being circumferentially spaced from the other scanning gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gage bar means and the xed gaging means responsive to the capacity between the gage bars due to the material passing therebetween, and indicator means connected with the `electronic circuit to indicate the capacity between the capacitive means due to the material passing therebetween; capacitive adjusting mechanism for each spiral scanning gage bar comprising adjust-ing means including a plurality of circumferentially spaced adjustable members, and a circumferentially short conducting means, one of said means being connected with its scanning bar for rotation therewith and the other means being fixed adjacent the path of rotation of the rotatable means, and the rotatable means being electrically connected with the spiral scanning bar and the xed means being electrically connected wtih the lfixed gaging bar, at least one standard comparator mechanism comprising a rotatable comparator bar of short circumferential dimension and connected with the scanning bar for rotation therewith and located in a circumferential gap between the scanning bars, a iixed comparator bar of short circumferential dimension located to be passed by the rotatable comparator bar as it rotates, and means electrically connecting the fixed comparator bar with the electronic circuit.

12. A gage to measure variations in a material comprising capacitive means including a fixed gaging means and scanning gaging means having a plurality of gage bars of spiral form and each bar being circumferentially spaced from the other scanning gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gage bar means and the iixed gaging means responsive to the capacity between the gage bars due to the material passing therebetween, and indicator means connected with the electronic circuit to indicate the capacity between the capacitive means due to the material passing therebetween; capacitive `adjusting mechanism for eachy scanning bar including a circumferentially short conducting member rotatable with each scanning bar, a plurality of circumferentially spaced members for each scanning b'ar and mounted adjacent to the path ofl rotation of the short conducting member, the conducting member being connected with the scanning bar and the circumferentially .spaced members being electrically connected .with the lix'ed bar, means to adjust the position 'of ea'ch circumferentially spaced member, at least one standard comparator mechanism comprising a rotatable comparator bar of short circumferential dimension and connected with the scanning b'ar for rotation therewith and located in a circumferential gap of the scanning bar, a xed comparator bar of yshort :circumferential dimension located to be -passed by the rotatable comparator bar as it rotates, and means electrically connecting a comparator bar with the electronic circuit.

13.A gage Ato Vmeasure variations in a coating upon a material comprising a first gage, the first gage `including 'a hxed gage bar, at least one scanning ,gage `ba`r means of spiral form mounted for rotation adjacent the fixed gage bar and spaced ktherefrom to pass a material therebetween, and an electronic circuit connected with the scanning gage bar means and the fixed gage bar responsive to the capacity therebetween due to the material passing therebetween, the electronic circuit including time delay means; and a second gage adapted to be spaced along the material from the first gage thereby resulting in a spaced timingin their readings, the second gage including a fixed gage bar, at least one scanning gage bar means of spiral form mounted for rotation adjacent the fixed gage bar and spaced therefrom to pass a material therebetween, and an electronic circuit con-f nected with the scanning gage bar means and the fixed gagerbar Vresp'onsiveto the capacity between the gage bars due to the materialy passing therebetween; and a cathode ray tube having beam deflecting means with the electronic circuit of each gage connected to the beam deflecting means in sbtractive relation to'indicate the thickness of the coating on the material.

14'. A gagey as in claim 13 in which the beam detlecting means of the cathode ray tube are oppositely disposedA plates, and the electronic circuit for one gage being connected with one plate, and the electronic circuit for the other gage being connected with the other plate.

l5. A gage as in claim 13 in which the time delay means is a recording mechanism having recording means and pick -up means, spaced from the recording means, and the Vspacing therebetween providing a time delay equalt'o the spaced time between the readings of the two gages.

16. A gage to measure variations in a material comprising capacitive means including a fixed gaging meaps and scanning gaging bar means of spiral form mounted for rotation adjacent the xed gaging means and spaced therefrom to pass a material therebetween and having a continuous circumferential extent of approximately 360, an electronic amplifying circuit connected with the scanning gaging bar means and the fixed gage bar responsive to the capacity between the means due to the material passing therebetween, a cathode ray tube indicator connected with the electronic amplifying circuit to indicate variations in the capacity between the capacitive means due to variations in the material passing therebetween and havinghorizontal sweep means for the beam, and a sweep circuit connected with the tube indicator sweep means including a pair of sets of condenser plates connected with the 4scanning gaging bar means tov be rotated thereby at twice the speed of rotation thereof and a pair of sets of fixed plates mounted for cooper-ation with the rotatable condenser plates.

17. A gage as in claim 16 including capacitive adjusting means for the spiral scanning bar means comprising a circumferentially short conducting member connected with the scanning bar means for rotation therewith and electrically connected therewith, and a plurality of circumferentially spaced adjustable members mounted adjacent to the path of rotation of the rotating conducting member and electrically connected with the fixed gaging means.

18. A gage as in claim 16 including blanking means driven by the scanning gaging bar means and connected in the electronic circuit to blank out the return beam trace on the cathode ray tube.

19. A gage as in claim 18 in which the blanking means is `a photoelectric cell, a lamp directing its light upon the cell, and a blanking plate driven with the condenser means and obstructing the light between the lamp and photocell for alternate revolutions of the scanning gaging bar means.

20. 4A gage as in claim 16 including capacitive adjusting means for the spiral scanning bar means comprising a circumferentiall-y short ,conducting member connected with the scanning bar means for rotation therewith and a plurality of circumfercntially spaced adjustable members 'mounted adjacent to the path of rotation ofthe rotating conducting member and electrically connected 1S with the fixed gaging means; and blanking means driven by the scanning gaging bar means and connected in the electronic circuit to blank out the return beam trace on the cathode ray tube.

2l. A gage to measure variations in a material cornprising capacitive means including a fixed gaging means and scanning gaging means having a pair of scanning gage bars of spiral form and each bar being circumferentially spaced from the other scanning gage bar, means mounting the scanning gage bars for rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected between each scanning bar and the fixed gaging means including an oscillator for each circuit generating a high frequency, the frequency generated by the oscillators having a ratio of at least two to one; and indicating means connected with the electronic circuits.

22. A gage as in claim 21 in which the indicating means is a cathode ray tube having vertical deflecting means and horizontal deliecting means, beam sweep means connected with the horizontal deliecting means, and the electronic circuits connected with the vertical defiecting means of the cathode ray tube.

23. A gage as in claim 21 including capacitive means connected with the scanning bar means and driven therewith and forming a part of the sweep circuit to synchronize the sweep of the beam with the rotation of the scanning means.

A gage to measure variations in a material comprising capacitive means including a fixed gaging means and scanning gaging means having at least one scanning gaging bar of spiral form, means mounting the scanning gaging bar for' rotation adjacent to the fixed gaging means and spaced therefrom to pass a material therebetween; an electronic circuit connected with the scanning gaging neans and the fixed gaging means comprising an oscillator including a tube having a grid and a plate, an oscillating circuit connected between the plate and grid and operating on the slope of its resonance curve, and a grid resistor; modulating means connected with the grid resistor, a second oscillator generating a carrier frequency connected with the modulating means, amplifying means connected with the modulating means including at least one amplifying tube have a grid and a bias resistor connected with the tube biasing the grid beyond cut off to a point to retain not more than`ten percent of the signal, and demodulating means connected with the amplifying means.

25. A gage as in claim 24 including capacitive adjusting means connected with one of the gaging means including a plurality of circumferentially spaced conducting members and a conducting member rotatable and connected with the scanning gaging means, amplifying means connected with demodulating means, and a cathode ray tube having vertical beam deflecting means connected with the next aforesaid amplifying means.

26. A gage as in claim 24 including horizontal beam defiecting means for the cathode ray tube, and a sweep circuit connected with the horizontal beam defiecting means including rotatable condenser driven by the scanning gaging means.

27. Apparatus for measuring the thickness of a coating applied to a moving strip comprising a first means adjacent said strip for obtaining an electrical impulse proportional to the thickness of the uncoated strip, a second means remote from the first means adjacent said strip for obtaining an electrical impulse proportional to the thickness of the coated strip, means for subtracting said first impulse from said second impulse to obtain a net impulse proportional to the coating thickness and for indicating the net impulse, and means for delaying the impression of said first impulse to said last named means until that portion of the uncoated strip originally gaged reaches said second means.

Cil

28. Apparatus for measuring the thickness of a coating applied to a moving strip comprising a first means adjacent said strip for obtaining an electrical impulse proportional to the thickness of the uncoated strip, a second means remote from the first means adjacent said strip for obtaining an electrical impulse proportional to the thickness of the coated strip, an indicator having means for subtracting said first impulse from said second impulse to obtain a net impulse proportional to the coating thickness, said subtracting means controlling the indicator to indicate the net impulse, and means for delaying the impression of said first impulse to said last named means until that portion of the uncoated strip originally gaged reaches said second means.

29. Apparatus for measuring the thickness of a coating applied to a moving strip comprising a first means adjacent said uncoated strip for obtaining a first electrical impulse proportional to the thickness of the uncoated strip, recording means responsive to the electrical impulse to record the proportional thickness of the uncoated strip, means responsive to the record to regenerate the electrical impulse at a delayed time interval corresponding to the time elapsed for the sheet to reach a second impulse means, a second means remote from the first means adjacent said coated strip for obtaining a second electrical impulse proportional to the thickness of the coated strip, and an indicator having means to which the regenerated first impulse is applied for subtracting said regenerated first impulse from said second impulse to obtain a net impulse proportional to the coating thickness, said indicator being controlled by the net impulse.

30, Apparatus for measuring the thickness of a coating applied to a moving strip comprising a first means adjacent said uncoated strip for obtaining a first electrical impulse proportional to the thickness of the uncoated strip, magnetic recording means responsive to the electrical impulse to record the proportional thickness of the uncoated strip, means responsive to the recording means to regenerate an electrical impulse at a delayed time interval corresponding to the time elapsed for the sheet to reach a second impulse means, a second means remote from the first means adjacent said coated strip for obtaining a second electrical impulse proportional to the thickness of the coated strip, and an indicator having means to which the regenerated first impulse is applied and having means to which the second impulse is applied for subtracting said first impulse from said second impulse `to obtain a net impulse proportional to the coating thickness, said indicator being controlled by the net impulse.

3l. Apparatus for measuring the thickness of a coating applied to a moving strip comprising a first means adjacent said strip for obtaining an electrical impulse across the width of the sheet proportional to the thickness of the uncoated strip, a second means remote from the first means adjacent said strip for obtaining an electrical impulse across the width of the sheet proportional to the thickness of the coated strip, means for subtracting said first impulse from said second impulse to obtain a net impulse proportional to the coating thickness and for indicating the net impulse, and means for delaying the impression of said first impulse to said last named means until that portion of the uncoated strip originally gaged reaches said second means.

References Cited in the file of this patent v UNITED STATES PATENTS (Other references on following page) 17 UNITED STATES PATENTS Cloud Dec. 21, 1943 Martin et al. Oct. 22, 1946 Montcalm Ian. 4, 1949 .Taggi May 31, 1949 Grob et al July 25, 1950 Taylor Jan. 9, 1951 Hagan Nov. 6, 1951 

